1. Field of the Invention
This invention relates to data replication and more particularly relates to reliably updating a data group in a data replication environment.
2. Description of the Related Art
Two important objectives of a data replication environment are first to maintain an accurate replica of a data group, and second to maintain a consistent replica of a data group. Maintaining accuracy requires that as data is copied from one storage medium to another, no errors are introduced. Maintaining consistency requires that as data is copied from one storage medium to another, no data is lost or omitted. Accuracy may be ensured in the case of data corruption or media failure by copying a consistent replica of the data from a backup source. Consequently, in a data replication environment, it is important to maintain an up-to-date copy of a data group.
There are two main types of data replication environments, a synchronous system and an asynchronous system. A synchronous system updates a second storage medium each time a first storage medium is updated. The update to the second storage medium is a part of the update transaction made on the first storage medium. Inconsistencies are less common in a synchronous system because less data is copied with each update to the second storage medium, and less time is required for the copy transaction to be completed. However, synchronous systems are often cumbersome because of the intense usage of network resources required to constantly update the second storage medium.
Asynchronous systems are often used as an alternative to synchronous systems. An asynchronous system copies an updated data group from a first storage medium to a second storage medium. The first storage medium does not send updates to the second storage medium until updates to the first storage medium are complete. Asynchronous systems are beneficial, because updates to the second storage medium are made less frequently. If one of the storage mediums fails during a data update, the data may be inconsistent. Additionally, if a consistent backup copy of the data is not available, data may be lost or corrupted as a consequence of system corruption or media failure.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method that reliably update a data group in a data replication environment. Beneficially, such an apparatus, system, and method would provide a highly consistent backup replica of data stored in a data storage environment.